The invention generally relates to a method of testing a seismic torsional vibration damper for serviceability; and more particularly to a method in which the damping factor of the seismic torsional vibration damper is determined and compared with known damping factors of "healthy" vibration dampers to determine the service suitability of the damper under test.
A seismic torsional vibration damper is to be understood as used herein as a type of torsional vibration damper which can be flanged or attached in the manner of a flywheel to a rotating system such as the crankshaft of an internal combustion engine having a tendency to vibrate. The damper carries on the periphery a partially rotatable mass, which vibrates during the rotation of the rotating system more or less strongly in opposite phase to the excitation vibration of the system capable of torsional vibration, and thereby damps this excitation of vibration.
In German Published Unexamined Patent Application (D-OS) 2,701,319, this torsional vibration damper is formed by a mass capable of torsional vibration, which is constructed as an inertia ring, and is coupled to the securing flange of the torsional vibration damper via an elastomeric intermediate layer. Such torsional vibration dampers are normally flanged to the crankshaft of internal combustion engines, to be precise mostly to the front shaft end, and thus not to the shaft end serving the driven side of the internal combustion engine. The torsional vibration dampers are designed to dampen excitation of vibrations occurring when certain speed ranges are exceeded.
In order to test the torsional vibration damper according to the teachings of the above-noted German reference, the damper was flanged to the crankshaft of an associated internal combustion engine, and the latter was put into operation. Before this, however, the torsional vibration damper was provided at the free end face with periodic, bright/dark marks, which were bounded with sharp edges and which lie within the same periphery both for the part flanged directly onto the crankshaft and for the inertia ring capable of torsional vibration. During the operation of the engine, optical sensors are used to scan the phase angles of the central part of the torsional vibration damper, which part is flanged to the crankshaft, and of the inertia ring. By using an electronic evaluation, it is possible to determine the torsional vibration vector of the crankshaft, and the torsional vibration vector of the inertia ring of the seismic torsional vibration damper, and also their mutual phase angles. The magnitude and the mutual phase angle of the torsional vibration vectors are the criteria for testing the torsional vibration damper for serviceability which are recommended according to the teachings of this German reference. If, at definite speeds, these values fall outside a range of values determined in advance with healthy torsional vibration dampers, this is an indication that the torsional vibration damper under test is no longer working properly.
It is a disadvantage of the known test method that it requires the respectively associated internal combustion engine, and that certain speed states must be run in an expensive fashion, to which purpose an engine test stand is occupied in a costly fashion for a certain time. A further disadvantage is that the method can be carried out only if both the part of the torsional vibration damper flanged to the crankshaft, and also the inertia ring coupled so as to be torsionally rotatable, are accessible externally.
It is an object of the present invention to provide a test method for determining the serviceability of a vibration damper in such a way that the required test apparatus is simpler and the testing can be carried out more quickly.
Additionally it is a further object of the present invention to provide a test method wherein it is also possible to test those torsional vibration dampers in which the inertia ring is not accessible externally.
These and other objects are achieved by providing a method wherein the damping factor of a seismic torsional vibration damper is determined and compared with known damping factors of "healthy" vibration dampers to assess the service suitability of the damper under test. In the method, a firmly clamped torsion-spring bar is employed to provide a relatively simple test setup. It is further supplemented only by a sensor for determining the amplitude of vibration, and by and electronic evaluator, as is, however, also necessary in the prior art. A special feature of the formation of criteria according to the invention consists in that it is not the extent of the damping which is determined and compared with the "healthy" torsional vibration dampers, but the steepness of its falling off from amplitude to amplitude. Surprisingly enough, it has namely emerged that, by contrast with the normal behavior of vibration dampers having a damper factor which is constant and thus independent of amplitude, the damping factor of viscosity torsional vibration dampers has a falling characteristic which is dependent on amplitude. This falling characteristic changes depending on the state of ageing of the viscous damping medium. It can be said on the basis of this that as long as the sequence of the damping factors determined falls in value and, moreover, lies inside a predetermined falling scatter band, the viscous damping medium may still be expected to have a long service life. Such viscosity torsional vibration dampers can be reused without hesitation in the case of testing.
Advantageous embodiments of the invention employ the amplitude of rotation angle of the torsion-spring bar although it is also possible to determine the accelerator amplitude in the region of the upper end of the torsion-spring bar to obtain the same results. Moreover, the invention is described in more detail below with reference to an illustrative embodiment represented in the drawings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.